Patent GB-1328087-A (GB)
Title: Pneumatically controlled medical respirators
IPC: A61M16/00
Filed: 1970-08-28
Abstract: 1328087 Respiratory apparatus PYE Ltd 28 Aug 1970 [15 Sept 1969] 45424/69 Heading AST A closed circuit, multi-mode respirator of the type described in Specification 1162151 has a pneumatic control unit adapted to periodically close, by pressure in the pipe 20 or 26, inhalation and exhalation control valves (86), (87), Fig. 2 (not shown), which are spring- biassed in an open position, thereby initiating inspiration and expiration periods of the respirator, which control unit may be responsive to one or more of the parameters, time, or pressure or volume of gas flowing to or from the patient. As shown, the control unit comprises a first change-over valve 13 having alternative outputs to pipes 14 and 22, an input from a source of air pressure 8 via a tube 12, and two control inputs 27, 28. The pipes 14, 22 are connected to the control inputs 15, 24 of a second change over valve 16 whose outputs are connected with the pipes 20, 26 operating the valves (86), (87) respectively. An inspiration gas circuit in communication with the input 27 comprises a pressure mode switch 35, a volume mode switch 36 and a time mode switch 37 connected in parallel between pipes 29 and 31, each switch being in series with a selector switch 32-34, the input 28 being in communication with a similar circuit but which is adapted to initiate an expiration period. One or more of the mode switches of each circuit may be made operable by placing the switch into communication with the pipes 31 or 38, which pipes are connected to the pipes 26, 20 respectively by means of the associated selector switch and in the event of the selected mode switch being actuated, the pipes 31 or 38 are placed in communication with the pipes 29 or 30 and thus the control input 27 or 28 of the valve 13 is subjected to the pressure of the pipe 26 or 20 causing the shuttle mechanism 71 to be moved through the body of the valve 13, admitting air pressure to the alternative outlet and changing the second valve 16 in a similar way to admit air pressure to the alternative pipe 26 or 20. The pressure switch 35 is operated by a downward movement of the diaphragm 45 which is subjected to pressure changes in the patient inspiration line (106), via a line 47, the switch 42 of the expiration circuit being, actuated by an upward movement of the diaphragm 46 via a line 50. The volume switch 36 is operated by a downward pivotal movement of the lever 52 about a point 51 caused by movement of the bar (84) of the respirator, the volume switch 43 being operated by a similar upward movement of the bar 54. The time switch 37 comprises a piston 69 which may be retained in the position shown by pressure in the pipe 31 and moved upwards by air pressure against the piston 70 caused by flow of air through a pipe 54 into a cylinder 56 via a flow restriction 75, e.g. a needle valve. The time taken for attainment of this required pressure is determined by the volume of the cylinder 56, relative size of the pistons &c. Upon actuation of the piston 69, the cylinder is vented through a low resistance one-way valve at 75 and vent 23 of the valve 13, the time switch 44 working in a similar way. In the event of more than one selector switch 32-34 and 39-41 being opened, the respirator cycles will be determined by the parameter reaching its prescribed value first in any half cycle.